The present invention relates to internode routing for a telephone system.
In the past, telephone systems, for example emergency or 911 telephone systems have been provided in order to route telephone calls from a caller to a Public Safety Answering Point (PSAP) in the case of an emergency. Such systems have utilized switching devices for routing the calls to the correct answering point.
Such 911 telephone service for an entire state has required multiple tandem switches, with each of the switches serving a geographical area. The state is thus divided into Emergency Service Zones (ESZ) in which some of the zones overlap two tandem service areas. The caller may originate into one 911 tandem, but the Emergency Service Agency is serviced by a second 911 tandem. Thus, it is necessary that the tandems must be capable of transferring the 911 call between them in order to properly route the telephone calls.